Due to the recent completion of the human and mouse genomes as well as advances in mouse technologies, there has been an enormous increase in the number of mouse mutants and models for human disease. Maintaining and distributing pathogen-free mouse strains is both labor-intensive and costly for individual investigators to sustain longterm. The NIH/NCRR recognized the need for a common repository and distribution center for genetically modified mice, and in 1999 they responded by funding the Mutant Mouse Regional Resource Centers (MMRRC). UNC-Chapel Hill is one of four MMRRC centers that are developing this resource for the benefit of the entire .biomedical community. Since the initial funding in 1999, a significant amount of effort has been invested in creating the organizational infrastructure and establishing standard operating procedures (SOPs) for importation, rederivation, phenotyping, cryopreservation and distribution of mutant mouse strains. In 2001, the MMRRC-UNC accepted its first strain and has experienced significant-expansionever since. In parallel with these efforts, the MMRRC has also taken advantage of the expertise available at UNC to bring new technologies and resources to the community such as mutant ES-cell lines, gnotobiotic strains and improved in vitro fertilization methods. To meet future demands for MMRRC services and improve upon existing technologies, this proposal aims to: (1) import, archive and distribute genetically modified mouse strains, (2) increase visibility of the MMRRC through advertising and solicitations targeting the biomedical research community, (3) develop improved and reliable methods for assisted fertilization, (4) integrate gnotobiotic strain development into MMRRC services (5) generate an allelic series of point mutations in genes of interest as a community resource.